CN110718630B - Method for improving performance of ferroelectric film capacitor - Google Patents

Abstract

The invention relates to a method for improving the performance of a ferroelectric film capacitor. During the process of applying a voltage to the film in the ferroelectric film capacitor by using a positive probe tip or a negative probe tip to read and write the ferroelectric film capacitor, the length of the pulse input by the tip is reduced to less than 2ms, and/or after the ferroelectric film capacitor is polarized by voltage, the voltage input by the tip is adjusted to 0V and maintained for a period of time, so as to improve the performance of the ferroelectric film capacitor. A method for improving the performance of a ferroelectric film capacitor according to the present invention is simple, easy to operate and low in cost, and solves the problems in the prior art that the ferroelectric film capacitor has poor fatigue resistance and slow reading and writing speed when a positive probe tip input voltage is used, and at the same time solves the problem that the reading and writing speed of a ferroelectric film capacitor needs to be further improved when using a negative probe tip input voltage, which is of great promotion value.

Description

A Method for Improving the Performance of Ferroelectric Film Capacitors

technical field

The invention belongs to the technical field of electronic devices and relates to a method for improving the performance of ferroelectric film capacitors.

Background technique

Capacitors are one of the widely used electronic components in electronic equipment and play an irreplaceable role in integrated circuits. Ferroelectric film capacitors are also widely used as a special capacitor. With the rapid development of electronic information technology, higher requirements are put forward for the performance of capacitor devices. Among them, the reading and writing speed is an important standard to measure the performance of capacitor devices. When a positive probe tip is used to input a voltage to a ferroelectric film capacitor, the ferroelectric film area under the point electrode or line electrode of the device diffuses, resulting in an increase in the polarization area. The regional polarization effect caused by the charge on the tip of the positive probe causes the "parasitic layer" of the capacitor to be generated, resulting in an increase in the reading and writing time of the ferroelectric film capacitor, and a slow reading and writing speed. Moreover, due to the appearance of the "parasitic layer", the effective thickness of the ferroelectric film that is already very thin is reduced, thereby reducing the remanent polarization. For the application of electric film capacitors, it is necessary to find suitable methods to avoid these problems, so as to achieve the purpose of improving the performance of ferroelectric film capacitors.

The doctoral dissertation "Study on the performance of poly(vinylidene fluoride-trifluoroethylene) ferroelectric nano-film and the mechanism of electroactive interface layer" introduced an interface layer (such as electronic conductor PEDOT/PSSH and ion conductor PVPA) between the ferroelectric film and the electrode layer to improve the performance of the ferroelectric film and the reading and writing speed, which had a certain effect, but because the interface layer needs to be introduced between the ferroelectric film and the electrode layer, it is relatively complicated and increases the operation process and cost; "Polarization reversal and fatigue characteristics of poly(vinylidene fluoride-trifluoroethylene) nano-film" ( Acta Physica Sinica, 2015, 64(16).) The improvement of ferroelectric properties can be achieved by controlling the humidity during annealing treatment and film formation, but the effect is relatively limited.

Patent CN98814030.6 discloses a ferroelectric capacitor and a semiconductor device. The capacitor is composed of an upper electrode, a ferroelectric film and a lower electrode. The ferroelectric film is a perovskite oxide containing a certain metal element, while the upper electrode and the lower electrode contain an intermetallic oxide composed of the metal element and a precious metal. This patent avoids the "parasitic layer" in the ferroelectric film and interface layer during voltage input by changing the electrode structure and using inorganic ferroelectric film materials, thereby improving the polarization performance of the ferroelectric film of the ferroelectric capacitor. The reverse speed is accelerated, and the reading and writing speed is also improved, but specific electrode materials are required, and the material selection and device preparation are relatively harsh; patent CN201710362281.9 discloses a non-volatile ferroelectric memory with high readout current and its operation method. The patent improves the readout current of the conductive domain wall of the non-volatile ferroelectric memory by increasing the perimeter of the conductive domain wall. It also improves the electrode structure and adds branch electrodes to operate. The experimental conditions are relatively complicated; patent CN20161055720 8.2 Aiming at the problem that ferroelectric thin film is used as the dielectric layer material of resistive variable memory, there is a relatively small switching ratio, and a ferroelectric resistive variable memory that can control the switching ratio is provided. By controlling the thickness of the ferroelectric thin film material during the preparation process, the ferroelectric domain pinning layer at the interface between the ferroelectric material and the bottom electrode material is adjusted. 38.9 discloses a non-volatile ferroelectric memory and its preparation method and read/write operation method. The ferroelectric memory includes a ferroelectric thin film layer and its surface etched ferroelectric memory unit and left and right read and write electrode layers arranged on both sides of the ferroelectric memory unit. It can realize non-destructive and fast readout of the stored electric domain logic information in a large current mode, but the device is relatively complicated and it is difficult to operate; patent CN201480015331.0 discloses a ferroelectric capacitor with improved fatigue and breakdown performance.

In addition, although the reading and writing speed is relatively fast when the input voltage of the negative probe tip is used, it still needs to be further improved.

Therefore, it is of great significance to study a simple, efficient and low-cost method to improve the performance of ferroelectric film capacitors, especially to improve fatigue resistance and increase read and write speed.

Contents of the invention

One of the purposes of the present invention is to solve the problems in the prior art that the ferroelectric film capacitor has poor fatigue resistance and slow reading and writing speed when using a positive probe tip input voltage. The second purpose is to solve the problem that the reading and writing speed of the ferroelectric film capacitor needs to be further improved when using a negative probe tip input voltage, and provide a method for improving the performance of the ferroelectric film capacitor.

In order to achieve the above object, the scheme adopted by the present invention is as follows:

A method for improving the performance of a ferroelectric film capacitor. During the process of applying a voltage to the film in the ferroelectric film capacitor by using a positive probe tip or a negative probe tip to read and write the ferroelectric film capacitor, the pulse length input by the tip is reduced to less than 2ms (in the prior art, the pulse length input by the tip is generally 10-20ms), and/or after the ferroelectric film capacitor is polarized by voltage, the voltage input by the tip is adjusted to 0V and then maintained for a period of time (in the prior art, it is generally not adjusted to 0V, and the applied voltage is not adjusted, but by adjusting the thickness of the film or changing the electrode. Improvement of materials and structures) to improve the performance of ferroelectric film capacitors.

After the positive tip voltage is input, the regional polarization effect caused by the positive tip charge causes the formation of a “parasitic layer” of the capacitor, which increases the reading and writing time of the ferroelectric film capacitor. The generation of the “parasitic layer” also reduces the effective thickness of the ferroelectric film, which is already very thin, thereby reducing the remanent polarization. At the same time, the defects formed will affect the fatigue resistance when the polarization is reversed in the future. Most of the existing technologies improve the performance of the capacitor by changing the structure of the ferroelectric film capacitor or the material of the ferroelectric film. problem.

The present invention does not need to make any changes to the material of the ferroelectric film or the structure of the capacitor, but only changes the voltage operation process conditions. One solution is to reduce the pulse length input by the tip to less than 2ms. Since the moving speed of the trapped charges is constant under the condition of a fixed external field strength, the moving distance of the trapped charges is proportional to the time. Therefore, the shortening of the pulse length is beneficial to reduce the moving distance of the trap charges; at the same time, the change of the pulse length will change the number of electrons injected by the high electric field of the interface layer, thereby affecting the amount of the generated trap charges. The degree of pinching is reduced, thereby improving the fatigue resistance of the capacitor, and the improvement of the fatigue resistance of the capacitor will increase the reading and writing speed of the capacitor;

Another solution is to adjust the tip input voltage to 0V after the ferroelectric film capacitor is polarized by voltage and keep it for a period of time. The purpose of this operation is: after a period of time, the tip will provide enough compensation charges to offset the positive or negative charges brought by the positive tip input or negative tip input, avoid further polarization of the ferroelectric film under the electrode, reduce the diffusion area of the ferroelectric film area under the device point electrode or line electrode, thereby making the polarized area smaller, effectively avoiding the "parasitic layer" of the capacitor caused by the regional polarization effect caused by the positive probe/negative probe tip charge. ", thereby reducing the read and write time of the ferroelectric film capacitor and improving the read and write speed of the ferroelectric film capacitor. In addition, the compensation charge provided by the tip will also enter the vicinity of the ferroelectric domain and gradually surround the insulator medium, so that the small ferroelectric domain generated due to frequent polarization reversals regains vitality, and then continues to participate in the reversal process, effectively reducing the depolarization field, increasing the residual polarization strength, and improving the fatigue resistance of the capacitor.

The mechanism of improving the reading and writing speed of the ferroelectric film capacitor when the input voltage of the negative probe tip is adopted by the method of the invention is the same as that of the reading and writing speed of the ferroelectric film capacitor when the input voltage of the positive probe tip is adopted. By adopting the method of the invention, on the one hand, the fatigue resistance of the ferroelectric thin film can be improved and the reading speed of the capacitor can be accelerated when the voltage is input to the positive tip;

As a preferred solution:

According to the method for improving the performance of the ferroelectric film capacitor, the reading and writing speed of the ferroelectric film capacitor is less than 1 μs.

According to a method for improving the performance of a ferroelectric film capacitor, the positive probe tip or the negative probe tip is a positive probe tip or a negative probe tip of a piezoelectric force microscope (PFM).

According to the method for improving the performance of a ferroelectric film capacitor, the ferroelectric film capacitor is an organic ferroelectric film capacitor or an inorganic ferroelectric film capacitor.

According to a method for improving the performance of ferroelectric film capacitors, the organic ferroelectric film capacitors are P(VDF-TrFE) polymer film capacitors, nylon-11 film capacitors, nylon-7 film capacitors or nylon-5 film capacitors.

A method for improving the performance of a ferroelectric film capacitor as described above, the P (VDF-TrFE) polymer film capacitor is a capacitor of a "sandwich" structure consisting of a top electrode, an intermediate P (VDF-TrFE) polymer film and a bottom electrode, the thickness of the P (VDF-TrFE) polymer film is 60nm, and the bottom electrode is metal Ti.

In the method for improving the performance of the ferroelectric film capacitor as described above, the pulse input by the tip is a single pulse, and five pulses are set as one cycle when the tip is input.

As mentioned above, a method for improving the performance of ferroelectric film capacitors, the pulse length of the tip input is 30μs-2ms, the absolute value of the tip input voltage is 8-10V, the voltage of the tip input is too high to cause breakdown, and the polarization is not obvious if it is too low.

As mentioned above, a method for improving the performance of ferroelectric film capacitors, a period of time is 30 to 100s, and a period of time is the recovery waiting time. By setting this time, according to the electron migration rate, the charge compensation can be effectively satisfied.

As mentioned above, a method for improving the performance of ferroelectric film capacitors, the absolute value of the tip output voltage is 3.2-9V, the scan speed of the tip output is 0.4Hz, and the resonance frequency of the tip output is 5kHz.

Beneficial effect:

(1) A method for improving the performance of ferroelectric film capacitors of the present invention is simple and easy to operate and has low cost;

(2) A method for improving the performance of ferroelectric film capacitors of the present invention can improve the read and write speed in a targeted manner;

(3) A method for improving the performance of a ferroelectric thin film capacitor according to the present invention can effectively improve the fatigue resistance of the ferroelectric thin film.

Description of drawings

Figure 1 is a schematic diagram of the experimental measurement conditions of the positive and negative tip input voltages (the "+" point in the figure represents the input point of the positive probe tip, and the "-" point represents the input point of the negative probe tip);

Fig. 2 is the topography figure (magnification is 15000 times) of the PFM of P (VDF-TrFE) polymer thin film when embodiment 1 does not apply voltage;

Fig. 3 is the topography figure (magnification is 5000 times) of the PFM of P (VDF-TrFE) polymer thin film when embodiment 1 does not apply voltage;

Fig. 4 is the topography figure (magnification is 5000 times) of the PFM of the P(VDF-TrFE) polymer film after embodiment 1 applies positive voltage;

Fig. 5 is the topography figure (magnification is 5000 times) of the PFM of the P (VDF-TrFE) polymer thin film after comparative example 1 applies positive voltage;

Fig. 6 is the topography figure (magnification is 15000 times) of the PFM of P (VDF-TrFE) polymer thin film when embodiment 2 does not apply voltage;

Fig. 7 is the topography figure (magnification is 5000 times) of the PFM of the P (VDF-TrFE) polymer thin film after embodiment 2 applies negative voltage;

Among them, Data type Z range is the maximum scanning range of the scanner in the z-axis direction, the x-axis and y-axis directions can vary between 500nm and 125μm, the z-axis direction is generally tens of nanometers, friction is the force when the probe is in contact with the film, and height is the height of the probe.

Detailed ways

The present invention will be further described below in combination with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Example 1

A method for improving the performance of ferroelectric film capacitors. As shown in Figure 1, the positive probe tip of a piezoelectric force microscope is used to apply a voltage of +8V to the film in a P(VDF-TrFE) polymer film capacitor with a width of 1.2um and a thickness of 60nm. 400nm) to read and write ferroelectric film capacitors, shorten the length of the pulse (single pulse) input by the tip to 2ms, and after the ferroelectric film capacitor is polarized by voltage, adjust the voltage input by the tip to 0V and keep it for 30s to improve the performance of the ferroelectric film capacitor.

The PFM topography of the film when no voltage is applied is shown in Figure 2 and Figure 3, and the PFM topography of the film after the positive voltage is applied is shown in Figure 4. The read and write speed of the ferroelectric film capacitor is 0.70μs.

Comparative example 1

A method for reading and writing a ferroelectric film capacitor. The ferroelectric film capacitor is the same as in embodiment 1, and the reading and writing process is basically the same as in embodiment 1. The difference is that the length of the pulse (single pulse) input by the tip is 3ms, and after the ferroelectric film capacitor is polarized by voltage, the voltage input by the tip is adjusted to 0V and then kept for 0s.

The PFM topography of the film after the positive voltage is applied is shown in Figure 5, and the reading and writing speed of the ferroelectric film capacitor is 4 μs.

Comparing Example 1 with Comparative Example 1, it can be seen that the reading and writing speed of the ferroelectric film capacitor of Example 1 is far greater than that of Comparative Example 1. As can be seen from the comparison of Fig. 4 and Fig. 5, the polarization area of the ferroelectric film in Fig. 5 is larger (dot/line is larger), and the polarization area of the ferroelectric film in Fig. 4 is smaller. The positive charge mobility brought by the input of the tip is very small. Because the charges are compensated in time in Example 1, the further polarization of the ferroelectric film under the electrode is avoided. However, in Comparative Example 1, because these charges are not compensated in time, the ferroelectric film under the electrode will be further polarized. The polarization area of the ferroelectric film increases under the electron microscope, and the increase in the polarization area leads to a decrease in read and write speed.

The present invention uses a relatively short polarization pulse and keeps the tip at 0V for a long time after polarization to obtain sufficient compensation charges from the tip, effectively avoiding the supply of "charge-induced polarization", and solving the problem of increased reading and writing time caused by the positive tip of the P(VDF-TrFE) polymer film capacitor.

Example 2

A method for improving the performance of ferroelectric film capacitors. As shown in Figure 1, a voltage of -8V is applied to the film in a P(VDF-TrFE) polymer film capacitor with a width of 1.2um and a thickness of 60nm (P(VDF-TrFE) polymer film capacitor is a capacitor with a "sandwich" structure composed of a top electrode, a middle P(VDF-TrFE) polymer film and a bottom electrode, and the bottom electrode is metal Ti) with a negative probe tip of a piezoelectric force microscope (input three negative points, and the distance between two adjacent points is 400nm) to read and write ferroelectric film capacitors, shorten the length of the pulse (single pulse) input by the tip to 2ms, and after the ferroelectric film capacitor is polarized by voltage, adjust the voltage input by the tip to 0V and keep it for 30s to improve the performance of the ferroelectric film capacitor.

The PFM topography of the film when no voltage is applied is shown in Figure 6, and the PFM topography of the film after the negative voltage is applied is shown in Figure 7. When the negative tip of the probe is input with voltage, the spot area on the surface of the P(VDF-TrFE) ferroelectric film is very small. When the negative tip is used to polarize, the charge will be deposited on the surface of the film, that is, around the probe tip. Compared with the positive charge, the electrons have higher mobility and they can disappear faster. There is no or less "charge-induced switching" and smaller dots/lines are obtained. Therefore, the reading and writing speed of the negative tip itself is faster. By using this method, the reading and writing speed will be further accelerated. The reading and writing speed of the ferroelectric film capacitor is 0.72μs.

Example 3

A method for improving the performance of ferroelectric film capacitors. In the process of applying +10V voltage to the film in the nylon-11 film capacitor (which has the same size and thickness as the P(VDF-TrFE) polymer film) to read and write ferroelectric film capacitors, the length of the pulse (single pulse) input by the tip is shortened to 1ms. After the ferroelectric film capacitor is polarized by voltage, the voltage input by the tip is adjusted to 0V and then held for 0s to improve the performance of the ferroelectric film capacitor.

The reading and writing speed of the ferroelectric film capacitor is 0.96μs.

Example 4

A method to improve the performance of ferroelectric film capacitors. In the process of applying a voltage of +9V to the film in the nylon-7 film capacitor (which has the same size and thickness as the P(VDF-TrFE) polymer film) by using the tip of the positive probe of a piezoelectric force microscope to read and write the ferroelectric film capacitor, the length of the single pulse input by the tip is reduced to 30 μs.

The reading and writing speed of the ferroelectric film capacitor is 0.83μs.

Example 5

A method for improving the performance of ferroelectric film capacitors. In the process of applying a voltage of -9V to the film in the nylon-5 film capacitor (which has the same size and thickness as the P(VDF-TrFE) polymer film) by using the negative probe tip of a piezoelectric force microscope to read and write the ferroelectric film capacitor, the length of the single pulse input by the tip is controlled to be 10ms.

The reading and writing speed of the ferroelectric film capacitor is 0.82μs.

Example 6

A method to improve the performance of ferroelectric film capacitors. During the process of applying a voltage of -10V to the film in the inorganic ferroelectric film capacitor (which has the same size and thickness as the P(VDF-TrFE) polymer film) to read and write ferroelectric film capacitors, the length of the pulse (single pulse) input by the tip is reduced to 200 μs. After the ferroelectric film capacitor is polarized by voltage, the voltage input by the tip is adjusted to 0V and held for 80s to improve the performance of the ferroelectric film capacitor.

The reading and writing speed of the ferroelectric film capacitor is 0.75μs.

Example 7

A method to improve the performance of ferroelectric film capacitors, in the process of applying +10V voltage to the film in a P(VDF-TrFE) polymer film capacitor with a width of 1.2um and a thickness of 60nm (P(VDF-TrFE) polymer film capacitor is a capacitor with a "sandwich" structure consisting of a top electrode, a middle P(VDF-TrFE) polymer film and a bottom electrode, the bottom electrode is metal Ti) using a positive probe tip of a piezoelectric force microscope to read and write a ferroelectric film capacitor. The length was shortened to 1.2ms, and after the ferroelectric film capacitor was polarized by voltage, the voltage input at the tip was adjusted to 0V and held for 75s to improve the performance of the ferroelectric film capacitor.

The reading and writing speed of the ferroelectric film capacitor is 0.84μs.

Claims (10)

1. A method for improving the performance of ferroelectric film capacitors is characterized in that: in the process of applying a voltage to the film in the ferroelectric film capacitor using a positive probe tip or a negative probe tip to read and write the ferroelectric film capacitor, after the ferroelectric film capacitor is polarized by voltage, the voltage of the tip input is adjusted to 0V and maintained for a period of time to improve the ferroelectric film capacitor performance. 2. A method for improving the performance of a ferroelectric film capacitor, characterized in that: in the process of applying a voltage to the film in the ferroelectric film capacitor using a positive probe tip or a negative probe tip to read and write the ferroelectric film capacitor, the pulse length of the tip input is reduced to below 2ms, and after the ferroelectric film capacitor is polarized by voltage, the voltage of the tip input is adjusted to 0V and maintained for a period of time to improve the ferroelectric film capacitor performance. 3. A method for improving the performance of a ferroelectric film capacitor according to claim 1 or 2, characterized in that the reading and writing speed of the ferroelectric film capacitor is less than 1 μs. 4. A method for improving the performance of ferroelectric film capacitors according to claim 1 or 2, wherein the positive probe tip or the negative probe tip is a positive probe tip or a negative probe tip of a piezoelectric force microscope. 5. A method for improving the performance of a ferroelectric film capacitor according to claim 1 or 2, characterized in that the ferroelectric film capacitor is an organic ferroelectric film capacitor or an inorganic ferroelectric film capacitor. 6. a kind of method improving ferroelectric film capacitor performance according to claim 5 is characterized in that, organic ferroelectric film capacitor is P (VDF-TrFE) polymer film capacitor, nylon-11 film capacitor, nylon-7 film capacitor or nylon-5 film capacitor. 7. a kind of method improving ferroelectric film capacitor performance according to claim 6, it is characterized in that, P (VDF-TrFE) polymer film capacitor is the capacitor of " sandwich " structure that is made up of top electrode, middle P (VDF-TrFE) polymer film and bottom electrode, the thickness of P (VDF-TrFE) polymer film is 60nm, and bottom electrode is metal Ti. 8. A method for improving the performance of a ferroelectric film capacitor according to claim 1 or 2, characterized in that the pulse input by the tip is a single pulse. 9. A method for improving the performance of a ferroelectric film capacitor according to claim 1 or 2, characterized in that the pulse length of the tip input is 30 μs-2 ms, and the absolute value of the tip input voltage is 8-10 V. 10. A method for improving the performance of a ferroelectric film capacitor according to claim 1 or 2, characterized in that the period of time is 30-100s.